1. Field of the Invention
The present invention relates to rolling bearings for use in compressors of automobiles and others, bearing parts used therein, and heat treatment methods thereof.
2. Description of the Background Art
In one heat treatment method, as a way of ensuring long life of a bearing part against rolling contact fatigue, a surface layer portion of the bearing part is subjected to carbonitriding, with ammonia gas, for example, added to the atmospheric RX gas for heating (disclosed, e.g., in Japanese Patent Laying-Open Nos. 8-4774 and 11-101247). This carbonitriding hardens the surface layer portion, and further generates residual austenite within the microstructure, thereby improving the rolling contact fatigue life.
However, since the carbonitriding involves diffusion, the bearing part needs to be held at high temperature for a long period of time, which may coarsen the microstructure, making it difficult to improve the anti-crack strength. Further, there is another problem of an increase of aged dimensional change due to the increased residual austenite.
It may be possible to use alloy steel to ensure a long rolling contact fatigue life, improve the anti-crack strength and prevent the increase of the dimensional change. However, using the alloy steel will increase the raw material cost.
As the environment of use of the bearings has become increasingly severe, future bearing parts will have to be used under the conditions of greater load and higher temperature than in the conventional case. To this end, a bearing part having long life against rolling contact fatigue, great anti-crack strength and excellent dimensional stability is required.